Electrical measuring apparatus



H. W. HITCHCOCK. ELECTRICAL MEASURING APPARATUS.

yAPPLICATION FILED OCT. I8, 1920.

Patented June 13, 1922..

. ATTORNEY HARRY W. HITCHCOCK, 0F NEW YORK, N. Y., SSIGNOR T0 AMERICAN TLPHONE AND TELEGRAPI-I Coll/[P tlTY7 A CORPORATION OF NEW YORK.

ELECTRICAL MEASURING APPARATUS.

v1920, there has been described a method andl means for determining the impedance of an electric circuit in which the potential of a two-phase generator has been applied to the real `line and to the artificial balancing line kby means of an inductive device known as a phase shifter. This invention isa modification of the arrangement shown inthe aforesaid co-pending application in that it pro-` vides an arrangement for applying the current from one of the phases of a twophase generator directly to the circuit to be measured without the interposition of an inductive arrangement such as the phase shifter referred to.

This invention Vwill be made clearer from the following description when rea-d in connection with the attached drawing, of which Figures 1 and 2 show two forms of embodiment of the invention.

ln the arrangement shown in Fig. 1, a submarine cable 15 is connected with the ratio arm R at the point 13, and an artificial line 16 is connected with the ratio arm R at the point 14. The two ratio arms R and R which are equal in magnitude are connected together at the point 12. Bridged across the points 13 and 14 and connected therewith by means of the conductors 17 and 18'A respectively is adistortionless amplifier 19, preferably of the thermionic type,pthe output side of which is connected b v means of conductors 20 and 21 with the movable coils caind 6 of the d vnamometers DR and DX. Gr represents a twophase sine wave generator comprising the windings 1 ,and 2. One terminal of `winding1 is' grounded andthe other termina-l is connected Ywith the field coil 8 of the dynamometer DRy whichis also connected with the midpoint 12 of thev ratio arms. One terminal of the other winding 2 of the said generator is grounded and the other termi- Specification of Letters Patent. Patented June 13, 19252..`

Application filed October 18, 1920. SeraivNo. 417,764. i

nal is connected with one terminal'of the field coil l of the dynamomcter DX, the other terminal of which is connected to ground through a resistance R in series with an artificial line 25. Since the combination of the resistance R and the artificial line 25 is designed to balance the combination of the resistance R and the line 15 in parallel with the resistance R and the artificial line 16, the value of resistance R is equal in magnitude to one-half of either R or l', and likewise the value of the artificial line 25 is equal in magnitude to one-half of either the. line 15 or the artificial line 16.

ln Fig. 2, the same designating symbols have been used to indicate parts .which are the same in Figs. 1 4and 2. The arrangement shown in Fig. 2 differs from that shown in Fig. 1 by the use of a phase balancer 26 instead of the combination of the resistance lR and the artificial line 25 shown in` Fig. 1 to equalize currents flowing through' the field coils 3 and 4t. The phasebalancer 26 comprises two windings, 27 and v28,the former of -which is connected in series with winding 1 of the generator G and the latter is connected in series with thewinding 2 of the said generator. Located within the core on` which these windings are placed is a rotor.` preferably of thel squirrel-cage type, which is adapted torotate therein. ln ac'- cordance with the principles well lknown to those. skilled'in the art, the action of this phase balancer tends to equalize substantially the currcnts'in the two phases and to maintain the desired phase relation.V

ln order to obtain the best results, it is important that the resistance component should be great relative to the inductive reactance. A Since the resistance of the circuit includes that of the ratio arms it is obvious that the'magnitude of the resistance cornponent may be increased by making the value of the ratio arms great. I

Having'in mind rthe foregoing description of the various parts that comprise the 4ar.- rangement shown in Figs. 1 and 2. and their relation to each other. the invention will be fully understood from the following description of its mode of operation.

Considering Fig. 1, let it be assumed that the generator G is applying a potentialbetween the midpoint 12 of the ratioarms and ground.I and also across the resistance R andthe artificial' line 25 to ground. c The y the resistance imbalance.

currents resulting from the application of the potentials of the two phases will cause a flow' of'current through the field coils 3 and 4t respectively of" the dynamorneter 13R and DX. Since the line 15 and the artificial line 16 are identical except for inagnitudes of the second order, the current in thelield coil will be at allitimes equal to twice the current in the line 15 and will be exactly in phase with it. Since the dynamometer Die isconnectedto the other phase ofthe generator` `in series with 4the artificial 'impedance comprisingthe resistance R and the artificial line 25, which are equal in value toitheiimpedance of the line, and-the' artilicial; line' is measured between the apex 12 ot the ratio arms and ground, the current in theV iield coil 11e will then be at all times equal tofthe current in the `field coil 3 of DR. but 90 degrees displaced from. it in phase. .It the impedance ofi the line 15 is exactly equal toftliat ofthe artilicial linelf,v there will be no. difference of potential across the points 13 and 111, and consequently, no current will flow through the movable coils 5 and 6 of the) diynamometers, and accordingly there wifllbe` no deflection: of the said coils. The input circuit of the amplifier should be ot exceedingly high resistance, so as to minimise the current iiow between. these two points.. Furthermore the current supplied to the lineiniay beheld constant by means of a generator' field regulator placed' in series with the input circuit of the amplifier.

Let it be assumed that there is a small resistance"imbalance betweenthe line- 15v and the artiii'cial line 16. This will cause a difference of potential across the pointsl 18 and lit-.which will cause a flow of current through the input circuit of the amplifier. The amplifier' current in the output side of the circuit will flow through the movable coils 5 and 6 which are serially connected. Since the imbalance is produced by a re* sistance. the current in the line will be in phaseA with the said difference of potential. The current in the line flows through the field coil 3 and the currents resulting -irom the difference of potential across the points 13 and 11i flow through the coils 5 and 6. Since the currents in the coils 3 and v5 arev in phase, they will be displaced by an amount proportional to the magnitude of Since the currents in the coils 4s and 6 are displaced 90 degrees in'phase,' no vdeflection will be produced by the dynamometer DX. Thus` the nature of the imbalance and its magnitude are known.

In a similar mannern a reactance unbalance between the line 15 and its lartificial rline 16 will produce a difference oi' potential across' the input side of `the amplifier 19 and the resultant current flowingthrough they movable' coils 5 and-6 will be V9() degrees displaced in phase'from the current flowing through the coil 3, but will be in phase with' DX the magnitudes of which willherproporf tional to the resistance and the reactance romponents oit the imbalance.

The mode o'l operation shown in Fig.v 2 is in generalthe same as that shownin Fig. 1. ln this arrangement, thephase balancer 26 takes the place` of' the impedance R plus the-artificial line 25shown in Fig. 1. Annyr tendency et the currents through the, windings 27; and 218 to vary would be counteracted by the operation of thisl device, and

thereby the currents in the windings 3 and 4 are maintained equal ininagnitude displaced in phase by degrees. Such an: arrangement torl maintaining the currents oi the two phases equal: is `loestadapted for; frequencies up, to lapproximately 50 orv 60` cycles. @onsequent-ly, v for measurements at higher irequencies,y the arrangement shown inFig. .1, is preferable.

ln order to clearly show the invention, there have been purposely omitted therefrom certain details` which` are well known,

to4 those skilled in theA art. Thus7 to inf crease the efficiency ot the. arrangement, a voltage regulating device should be con.

necte'd with the generator in order tol ensurev constancy or' voltage. Furthermore, some and.

torna off current regulating device Should'lbe connected with` `the circuit of the dynar mometer field coils'in'order to ensure conf stancy of the current flowing therethrough. It will be seen frorntheforegoing that this invention provides means for the! direct measurement oil the resistance and. the reactance components of the impedance not only ot' a circuit. such as is; shown, but also of all types of circuits and apparatus.

Although this invention has been lldisclosed incertain particularv forms of' embodiment. it is apparent that itis capable` of embodiment in othery and different forms without departing Jrorn the spirit and scopre p of the appended claims.

What is claimed is:

1. 1n an electrical measuring device, the combination with an impedance of a Vsecond impedance adjusted to approximately lbalance electrically said rst impedance, a source of two-phase potential having one phase windingconnected with' said impedances in parallel', and the second phase wind-` ing connected with a current-balancing ar rangement. and means connected with said impedances and` said source of'potential to indicate the nature and magnitude of the imbalance existing between said impedances.

2. ln an electricalv measuring device, *the combination with a line of an artificial line adjusted to approximately balance electrically the said line, a source of two-phase po tential haring' one phase connected with the said line and the said artificial line in parallel andthe second phase connected with means to equalize the current in bothphases, and means connected with the said line and the said artificial line and With the said source of potential to indicate the imbalance between the said line and the said artificial line.

3. ln an electrical measuring device, the combination with a line of an artilicial. line adjusted to approximately balance electrically the said line, ratio arms connecting said line and said artificial line in parallel, a plurality oit electrical indicating instruments, a two-phase source of potential having one phase connected through the field Windingof one instrument to the ratio arms, and the other phase connected through the eld Winding of the other instrument to a device for equalizing` the currents in both phases and means lbridged across the said ratio arms to impress upon the movable coils of said instruments any difference of potential existing across said ratio arms.

Il. ln an electrical measuring device, the combination With a line of an artificial line adjusted to approximately balance electrically the said line and correlated by means of ratio arms, a second artificial line designed to approximate electrically the said line and the said first artificial line in parallel, a twopliase generator having one phase connected 'Wi th the said ratio arms and the other phase With the said second artificial line and indieating means connected with the said source and the said ratio arms adapted to show the magnitude and the nature of the unbalance between the said line and the said artificial line. i

In testimony whereof, I have signed my name to this specification this 15th day of October l920.` y

HARRY W. HITCHCOCK. 

